Lamp failure detection circuit

ABSTRACT

A circuit for monitoring for the failure of one or more lamps in an indicator device, a segment type readout device, or the like. Upon failure of a lamp, a silicon controlled rectifier or a transistor switch is biased into a conducting state to energize either a back-up lamp or a warning lamp. A circuit may be included to flash either the back-up lamp, the warning lamp or a third indicator lamp in response to detecting the failure of a lamp. When the circuit monitors a plurality of lamps, the circuit can be adapted to deactivate all lamps upon detecting the failure of any of the lamps.

United States Patent Malekzadeh 1 June 20, 1972 LAMP FAILURE DETECTION CIRCUIT All Asghar Mnleltndeh, Costa Mesa, Calif.

Master Specialties Company, Costa Mesa, Calif.

Filed: March 30, 1970 Appl. No.: 13,936

Related [1.8. Application Date Continuation-impart of Ser. No. 840,174, July 9, 1969, abandoned.

Inventor:

Assignee:

Relerenees Cited UNITED STATES PATENTS 5/1970 Pascente ..340/2$1X 6/1962 Weiss ..340/251X Primary E.\'aminerDavid L. Trafton Attorney-Owen & Owen 57 ABSTRACT A circuit for monitoring for the failure of one or more lamps in an indicator device, a segment type readout device, or the like. Upon failure of a lamp, a silicon controlled rectifier or a transistor switch is biased into a conducting state to energize either a back-up lamp or a warning lamp. A circuit may be included to flash either the back-up lamp, the warning lamp or a third indicator lamp in response to detecting the failure of a lamp. When the circuit monitors a plurality of lamps, the circuit can be adapted to deactivate all lamps upon detecting the failure of any of the lamps.

4 Claims, 4 Drawing Figures PATENTEUJWQ m2 INVENTOR: AL! A MAL EKZADEH.

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PliTENTlinJunzo m2 SHEEI 2 [If 2 Gama-(Qu nn .ATTYE LAMP rmunr: DETECTION CIRCUIT CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 840, l 74, filed July 9, I969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to devices using indicator lamps and, more particularly, to a circuit responsive to the failure of one or more indicator lamps for energizing either a back-up indicator lamp or a warning lamp.

An annunciator consisting of a group of warning indicator lamp assemblies is commonly provided in aircraft in controls mounted adjacent the pilot. Each lamp assembly is responsive to indicate the occurrence of a separate monitored condition or abnormality. The use of indicators is also of increasing importance in the military, space and industrial fields. For reliability, the typical indicator assembly has at least two lamps mounted to illuminate a translucent legend plate. The lamps are electrically connected in parallel so that the failure of one lamp will not give rise to a false indication of safety. There are, however, disadvantages to connecting indicator lamps in parallel. Since the lamps are simultaneously energized, these indicator assemblies have a relatively high power drain when energized. Furthermore, there is still a danger that the lamps will fail about the same time because the lamps have the same design life and are always operated together. Prior art indicator assemblies are usually tested by closing a switch to simulate the monitored condition or abnormality and then checking that the indicator legend plate is evenly illuminated. The failure of one or more of a number of lamps results in dark spots on the legend plate.

A plurality of indicator lamps are also commonly used in projection readout devices and in segment type readout devices. In the segment type readout device, for example, a number of prearranged segments are selectively illuminated to form the numbers zero through nine. With these devices, there is a danger that an erroneous number will be formed when one or more of the lamps fail. If the lamps are energized to form the number 7 and the upper lamp fails, the readout device will actually form the number 1". The efi'ect of this erroneous indication is compounded since the person using this information will rely upon the number l" as being correct. To date, the only method for checking segment type readout devices has been to simultaneously energize all lamps and then to check for any lamp failures. This will not, however, indicate a lamp failure after the test has been made.

SUMMARY OF THE INVENTION The instant invention is directed to a circuit for detecting the failure of an incandescent lamp, or of one or more of a plurality of incandescent lamps, and for energizing either a backup lamp or a warning lamp upon detection of a failure. The circuit can be used to provide an indicator assembly in which a single primary lamp is illuminated upon the occurrence of a monitored condition with the reliability of an indicator assembly in which two lamps are simultaneously illuminated. The back-up lamp is connected in series with an electronic switch and is connected to operate from the power source for the primary lamp. As long as the primary lamp operates, the electronic switch is biased into a nonconducting state. A failure of the primary lamp biases the switch into a conducting state to energize the back-up lamp.

In one embodiment of the invention, the electronic switch includes a silicon controlled rectifier which is connected in series with the back-up lamp. The primary lamp is connected to a power source through a series resistor. The controlled rectifier and the series connected back-up lamp are connected in parallel with the primary lamp and in series with the resistor. The gate electrode of the controlled rectifier is connected to a voltage divider which is in turn connected across the power source. As long as the primary lamp is illuminated, the voltage drop across the resistor reverse biases the controlled rectifier to prevent conduction by the controlled rectifier. Upon failure of the primary lamp, the voltage drop across the series resistor ceases and the controlled rectifier is triggered to energize the back-up lamp. A test circuit is provided to simultaneously test both the primary lamp and the back-up lamp. A conventional "bright-dim" circuit, such as the circuit shown in 0.8. Pat. No. 2,769,970, may be provided when the indicator assembly is used in aircrafi or in other applications where reduced light output is required for night-time operation.

In a second embodiment of the invention, the primary indicator lamp is connected in one leg of a voltage divider to provide the base bias for a normally conducting first transistor. The first transistor is biased into a nonconducting state upon failure of the primary indicator lamp. A normally nonconducting second transistor, which is connected in series with the back-up lamp, is controlled by the first transistor. The second transistor is biased into a conducting state when the first transistor is biased off by the failure of the primary indicator lamp. A test circuit is again provided to simultaneously energize both the primary and back-up lamps and a conventional dimming circuit may be provided for nighttime operation. A unijunction transistor flasher circuit may also be connected to flash either the back-up lamp or to flash a third indicator lamp when the primary lamp fails. If a third indicator lamp is used, it can be connected as a master warning lamp to flash upon the failure of any one of a number of primary indicator lamps.

When a plurality of incandescent lamps are to be simultaneously monitored, each lamp is connected to a separate electronic switch. The electronic switches are then connected in parallel to energize a single warning lamp upon failure of any of the plurality of lamps. The circuit may include an additional switch responsive to the parallel electronic switches to remove the power from either selected ones of or all of the plurality of lamps. Thus if the lamps are in a segment type readout device and any lamp fails, the power can be removed from all of the lamps to prevent the possibility of an erroneous readout indication.

Accordingly, it is a primary object of the invention to provide a circuit for detecting the failure of an incandescent lamp and for energizing either a back-up lamp or a warning lamp in response to the detection of a failure.

Another object of the invention is to provide a reliability circuit for an indicator lamp assembly in which a primary lamp is energized upon the occurrence of a monitored condition and in which a back-up lamp is energized upon the failure of the primary lamp.

Another object of the invention is to provide an indicator lamp assembly having the power drain of a single lamp indicator and the reliability of a dual lamp indicator.

Still another object of the invention is to provide a circuit responsive to the failure of any of a plurality of indicator lamps for energizing a warning lamp and removing power from the indicator lamps.

Other objects and advantages of the invention will become apparent from the following detailed description, with reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a detailed schematic circuit diagram of a preferred embodiment of an indicator lamp reliability circuit according to the instant invention;

FIG. 2 is a detailed schematic circuit diagram of a second preferred embodiment of an indicator lamp reliability circuit according to the instant invention;

FIG. 3 is a detailed schematic circuit diagram of an indicator lamp reliability circuit similar to FIG. 2, but with the polarity of the power source reversed and with the addition of a second back-up lamp and a flasher circuit for the second back-up lamp; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a preferred embodiment of the indicator lamp reliability circuit is shown in detail. A battery or other suitable direct current power source is connected to apply a voltage between a negative terminal 11 and a normally open fault switch 12. The switch 12 may be connected to monitor a particular condition, such as low fuel level or low oil pressure in an aircraft, and is closed upon the occurrence of the monitored condition. A voltage is applied to a positive buss 13 upon closure of the fault switch 12. A primary indicator lamp 14 is connected in series with a resistor 15 between the positive bus 13 and the negative terminal 11. The input and output terminals of a silicon controlled rectifier 16 and a back-up indicator lamp 17 are connected in series with each other and in parallel with the primary indicator lamp 14. A voltage divider including two series resistors 19 and 20 is connected between the buss 13 and the terminal 11 with the gate electrode of the controlled rectifier 16 connected to the common junction between the resistors 19 and 20. When the fault switch 12 is closed and the primary indicator lamp I4 is energized, there will be a sufficient voltage drop across the resistor 15 to counteract the voltage drop across the resistor 20 and thereby keep the controlled rectifier 16 biased in a nonconducting state. If, however, the primary lamp 14 should fail, there will be no current through the resistor 15 and the cathode of the controlled rectifier will be at the potential of the negative tenninal 11. The voltage appearing across the resistor 20 will then appear between the gate terminal and the cathode of the controlled rectifier 16 to trigger the rectifier 16 and thereby energize the back-up indicator lamp 17. The controlled rectifier 16 will remain in a conducting state until either the switch 12 is opened or voltage is removed from the circuit while changing the lamp 14.

A test switch 21 is provided for simultaneously testing the primary lamp 14 and the back-up lamp 17. A diode 22 is connected in series with the test switch 21 to prevent energization of either the primary lamp 14 or the back-up lamp 17 in the event that the polarity of the battery 10 is reversed. When the test switch 21 is closed, a voltage is applied from the battery 10 through the diode 22 and an isolation diode 23 to the positive bus 13 for energizing the lamp 14 and a voltage is simultaneously applied directly through the diode 22 to energize the back-up lamp 17. The diode 23 isolates the back-up lamp 17 from the buss 13 when the test switch 21 is open.

Turning now to FIG. 2, a modified embodiment of the indicator lamp reliability circuit is shown wherein the normally nonconducting controlled rectifier 16 of FIG. 1 is replaced by a normally conducting PNP transistor 25 and a normally nonconducting PNP transistor 26. A battery 27 is connected between a positive ground terminal 28 and a negative bus 29. A normally open fault switch 30 is closed to connect a bus 31 to the positive ground terminal 28 upon the occurrence of an associated monitored condition. A primary indicator lamp 32 is connected to the negative buss 29 and through a series bias resistor 33 to the buss 31. Thus, when the fault switch 30 is closed, current will flow through the primary indicator lamp 32 and the resistor 33 to illuminate the lamp 32. The base of the transistor 25 is connected to the common junction between the lamp 32 and the resistor 33 while the collector is connected through a resistor 34 to the negative bus 29 aNd the emitter is connected directly to the bus 31. As long as the lamp 32 is operating, the lamp 32 and the resistor 33 function as a voltage divider to maintain the base of the transistor 25 at a voltage between the negative bus 29 and the bus 31 and thereby bias the transistor 25 into a conducting state. Failure of the lamp 32 will raise the base voltage on the transistor 25 to the positive voltage on the bus 31 and thereby bias the transistor 25 into a nonconducting state. The collector of the transistor 25 is connected directly to the base of the transistor 26 while the emitter of the transistor 26 is connected to the bus 31 and the collector is connected through a back-up lamp 35 to the bus 29. As long as the transistor 25 conducts, the base of the transistor 26 will be near the positive potential on the bus 31 and the transistor 26 will be biased into a nonconducting state. When failure of the lamp 32 causes the transistor 25 to be biased into a nonconducting state, the base of the transistor 26 is connected through the resistor 34 to the negative bus 29, thereby biasing the transistor 26 into a conducting state to energize the back-up lamp 35. A test circuit is provided similar to that provided in FIG. 1. Upon closure of a test switch 36 the bus 31 is connected through a diode 37 to the ground terminal 28 to energize the primary lamp 32 and the junction between the back-up lamp 35 and the collector of the transistor 26 is connected through an isolation diode 38 to the ground terminal 28 to energize the back-up lamp 35.

Referring now to FIG. 3, the embodiment of FIG. 2 is shown but with the polarity of the battery 27 reversed. With the battery 27 reversed, the buss 29 becomes positive and the ground terminal 28 becomes negative. For the circuit to operate, it is only necessary to change the PNP transistors 25 and 26 of FIG. 2 to NPN transistors and to reverse the polarity of the isolation diodes 37 and 38 in the test portion of the circuitry.

FIG. 3 has also been modified by the addition of a warning lamp 40 which is flashed whenever the back-up lamp 35 is energized. When the lamp 35 is energized, a voltage is applied from the junction between the back-up lamp 35 and the collector of the transistor 26 through a diode 41 to a bus 42 to operate a unijunction flasher. A first base of a unijunction transistor 43 is connected through a resistor 44 to the buss 29 while a second base is connected directly to the bus 42. The emitter of the unijunction transistor 43 is connected through a resistor 45 to the bus 29 and through a capacitor 46 to the base of an NPN transistor 47. The base of the transistor 47 is also connected through a bias resistor 48 to the positive bus 29 while the emitter is connected to the buss 42 and the collector is connected in series with the second back-up lamp 40 to the buss 29. When failure of the primary indicator lamp 32 causes the back-up lamp 35 to be energized and a voltage is applied to the bus 42, the unijunction transistor 43 will be alternately switched on and off to alternately switch the transistor 47 off and on and thereby flash the warning lamp 40. It will be appreciated that the use of the isolation diode 41 permits a number of indicator circuits, each including a primary indicator lamp 32 and a back-up lamp 35, to be connected in parallel to a single flasher circuit containing a warning lamp 40 so that the failure of any one of the primary lamps 32 will cause the warning lamp 40 to be flashed.

Turning now to FIG. 4, a circuit is shown for simultaneously monitoring a plurality of incandescent lamps. A suitable power source is connected between a positive buss 50 and a negative ground terminal 51. A plurality of lamp modules 52, one for each monitored lamp 53, are connected in parallel between the positive bus 50 and the ground terminal 51. Each lamp module includes an electronic switch consisting of a pair of NPN transistors 54 and 55.

The lamp 53in each module 52 is connected in series with a resistor 56 between a lamp power bus 57 and a terminal 58. Each lamp 53 is energized by closing an associated switch 59 to ground the terminal 58. When energized, the series lamp 53 and resistor 56 form a voltage divider for biasing the base of the transistor 54 such that the transistor 54 is in a normally conducting state. The emitter of the transistor 54 is connected to the terminal 58 and the collector is connected through a resistor 60 to the positive buss 50. The transistor 55 has a collector connected to a bus 61, a base connected to the collector of the transistor 54 and an emitter connected to the terminal 58. When the switch 59 is closed and the transistor 54 conducts, the base of the transistor 55 is near ground potential and the transistor 55 is biased into a nonconducting state. In the event of a failure of the lamp 53, the potential on the base of the transistor 54 drops, switching the transistor 54 into a nonconducting state and the transistor 55 into a conducting state. Conduction by the transistor 55 in any of the modules 52 connects the bus 61 to the ground terminal 51.

When the failure of any of the lamps 53 causes the bus 61 to be grounded, a warning lamp 62 connected between the positive buss 50 and the buss 61 is energized to annunciate the failure. Grounding the bus 61 also biases a pair of normally conducting transistors 63 and 64 into nonconducting states. The bus 61 is connected through a resistor 65 to the base of the NPN transistor 63 and then through a series resistor 66 to the ground terminal 5 1. The emitter of the transistor 63 is connected through a forward biased diode 67 to the ground terminal 51. The forward voltage drop of the diode 67 determines the emitter bias of the transistor 63. A resistor 68 is connected in parallel with the warning lamp 62 for normally maintaining the bus 61 at a positive voltage. The resistor 68 main tains this voltage even though the warning lamp 62 may fail. The series resistors 65 and 66 form a voltage divider for biasing the transistor 63 into a normally conducting state. Upon failure of any of the lamps 53, the bus 61 is grounded, grounding the base of the transistor 63 to bias the transistor 63 into a nonconducting state.

The collector of the transistor 63 is connected through a resistor 69 to the base of a transistor 64. The base of the transistor 64 is also connected through a resistor 70 to the positive bus 50, while the emitter is connected to the positive buss 50 and the collector is connected to the lamp power bus 57. Conduction by the transistor 63 biases the transistor 64 into a conducting state to apply power from the positive bus 50 to the lamp power bus 57. When one or more of the lamps 53 fail, the transistor 63 switches the transistor 64 into a nonconducting state to remove power from the lamp power bus 57. A resistor 71 is connected between the positive bus 50 and the lamp power bus 57, in parallel with the transistor 64, to apply sufficient power to the bus 57 to restart the circuit afier all faulty lamps have been replaced. If it is desired to have one or more of the lamps 53 operable, even though one or more of the lamps 53 fail, those lamps are connected to the positive buss 50 instead of the lamp power buss 57.

A test switch 72 is provided for simultaneously testing all of the lamps 53 and the warning lamp 62. Closure of the test switch 72 connects a buss 73 to the ground terminal 51. The

junctions between each lamp 53 and its series resistor 56 are connected to the bus 73 through isolation diodes 74. The buss 61 is connected to the bus 73 through an isolation diode 75 for energizing the warning lamp 62. The collector of the transistor 63 is connected to the bus 73 through a diode 76 for maintaining the transistor 64 in a conducting state during the test.

It will be appreciated that various modifications and changes may be made in the four above described embodiments of the lamp failure detection circuit without departing from the spirit and the scope of the appended claims.

What is claimed is:

l. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps comprising, in combination, an indicator lamp, a plurality of normally nonconducting electronic switches, means connecting said switches in parallel with each other and in series with said indicator lamp whereby closure of any of said switches energizes said indicator lamp, means for energizing a different one of said switches in response to a failure of a difl'erent one of the incandescent lamps, and means responsive to the energization of any of said switches for disconnecting power from selected ones of the incandescent lamps.

2. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim 1, and including means for simultaneously energizing all of the incandescent lamps and said indicator lamp for simultaneously testing the incandescent lamps and said indicator lamp.

3. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim 1, and including switch means for selectively energizing each of the incandescent lamps.

4. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim I, wherein said disconnecting means disconnects power from all of the incandescent lamps. It a 

1. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps comprising, in combination, an indicator lamp, a plurality of normally nonconducting electronic switches, means connecting said switches in parallel with each other and in series with said indicator lamp whereby closure of any of said switches energizes said indicator lamp, means for energizing a different one of said switches in response to a failure of a different one of the incandescent lamps, and means responsive to the energization of any of said switches for disconnecting power from selected ones of the incandescent lamps.
 2. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim 1, and including means for simultaneously energizing all of the incandescent lamps and said indicator lamp for simultaneously testing the incandescent lamps and said indicator lamp.
 3. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim 1, and including switch means for selectively energizing each of the incandescent lamps.
 4. A circuit for detecting and indicating the failure of any of a plurality of incandescent lamps, as defined in claim 1, wherein said disconnecting means disconnects power from all of the incandescent lamps. 